RE: [Histonet] mouse vs. rat in situ; overfixed vs. poorfixed

From:"Favara, Cynthia (NIH/NIAID)"

I had one researcher that did a lot of in-situ with chromagens. We fix in
NBF and the conclusion was the longer the fixation time the better the
signal. Oh yes this was in mice.

Cynthia Favara
903 South 4th Street
Hamilton, MT 59840

-----Original Message-----
From: []
Sent: Friday, April 16, 2004 12:53 PM
Subject: [Histonet] mouse vs. rat in situ; overfixed vs. poorfixed

Dear All,

Recently I have tried radioactive in situ hybridization on mouse brain
with mouse-cfos riboprobe. I found that with same in situ protocol, the
of mouse is lighter than the signal of rat-cfos on rat tissue (to reach the
similar intensity, I need to lay down the film on mouse tissue longer time
twice much as on rat tissue.) I am not sure if it is normal for mouse tissue
get lighter signal or the rat in situ protocol just is not optimal for
Any suggestion? If I need to modify my rat protocol for mouse, what aspect
should I change?    

The second question is kind of interesting. Still about in situ, I tried two
situ on mouse brain tissue (the tissues are two copies from same animals,
and I
use same in situ protocol). The staining solutions are all the same except
4% PFA I used to fix the tissue. In the first staining I used a three-month
PFA, and in the second staining I made fresh PFA. The signal of second
is still kind of light but much more intense than the signal from first
staining. My conclusion is in the first staining the tissue was poor fixed
because stale PFA was degraded. So to improve the staining, I will try fresh
PFA with longer fixing time. But one of my collegue has a exactly contrary
opinion. He thinks in the first staining, the tissue was over fixed becuase
old PFA became more concentrated. So he suggest using fresh PFA and shorter
fixing time. By the way, the PFA was stored in a caped container in fridge.
Well, same fact but totally different viewpoints. Any comment?


Pengwei Yang

Biopsychology Program
University of Michigan         

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